1. Field of the Inventions
The present invention relates to a transmission apparatus that receives an optical signal by selecting any one of a plurality of provided optical signal transmission paths through protection control, and to a transmission apparatus and a path selection method of a transmission apparatus that are suitable when used, for example, in performing protection control in a WDM (Wavelength Division Multiplexing) apparatus.
2. Description of the Related Art
FIG. 4 is a view for describing the first mode of protection control in a conventional WDM transmission. In FIG. 4, numerals 100 and 200 represent a WDM transmitting apparatus and a WDM receiving apparatus, respectively. Also, two paths 301, 302 for protection control are provided in the optical transmission direction from the WDM transmitting apparatus 100 towards the WDM receiving apparatus 200, thereby enhancing the anti-obstruction property of optical communication between the WDM transmitting apparatus 100 and WDM receiving apparatus 200. Here, paths 301, 302 are constituted, for example, of optical fibers, relay amplifiers, and the like.
Namely, the WDM transmitting apparatus 100 includes n transmitting-side protection processing sections 130-1 to 130-n (in FIG. 4, illustration is made by keeping an eye on 130-1) provided in correspondence with the number of wavelengths capable of being transmitted by wavelength multiplexing [for example, n frequencies of f1 to fn (n; integer of 2 or more)], and wavelength multiplexing sections 141, 142 that perform wavelength multiplexing in correspondence with the paths 301, 302 for transmission with respect to optical signals of wavelengths f1 to fn from the respective transmitting-side protection processing sections 130-1 to 130-n. Here, in the following, with respect to the configuration of the transmitting-side protection processing sections 130-1 to 130-n, description will be given by keeping an eye on the transmitting-side protection processing section 130-1.
Here, the transmitting-side protection processing section 130-1 includes an optical coupler 131 that divides the optical transmission signals before wavelength multiplexing into two branches, and signal processing sections 132, 133 that perform signal processing on the respective optical transmission signals divided into two branches by the optical coupler. 131. The optical signal from the signal processing section 132 is outputted to the wavelength multiplexing section 141, and the signal from the signal processing section 133 is outputted to the wavelength multiplexing section 142.
This allows that the optical signals subjected to wavelength multiplexing in the wavelength multiplexing sections 141, 142 are outputted to a receiving section 220 of the WDM transmission apparatus 200 through the paths 301, 302 made of optical fibers, relay amplifiers, and the like. Here, in the signal processing sections 132, 133, numerals 132A, 133A are O/E (Optic/Electric) converting sections, and numerals 132B, 133B are NB·E/O (Electric/Optic) converting sections.
Also, the WDM receiving apparatus 200 includes wavelength separating sections 231, 232 that perform wavelength separation on the optical signals from the WDM transmission apparatus 100 that have been transmitted respectively through the paths 301, 302 into optical signals of wavelengths f1 to fn, and n receiving-side protection processing sections 240-1 to 240-n that perform receiving-side protection processing on the optical signals of respective wavelengths f1 to fn that have been separated in the wavelength separating sections 231, 232. Here, in the following, with respect to the configuration of the receiving-side protection processing sections 240-1 to 240-n, description will be given by keeping an eye on the receiving-side protection processing section 240-1.
Here, the receiving-side protection processing section 240-1 is configured to include signal processing sections 241, 242 that perform signal processing respectively on the optical signals of the same wavelength that have been subjected to wavelength separation in the wavelength separating sections 231, 232, an optical switch 244 that selectively outputs either one of the optical signals from the signal processing sections 241, 242 as an active optical signal, and an optical switch controlling section 243 that controls the optical switch 244.
Further, the signal processing sections 241, 242 respectively include O/E converting sections 241A, 242A that convert the optical signals from the wavelength separating sections 231, 232 into electric signals and extract supervision control information needed for protection control, and E/O converting sections 241B, 242B that convert the electric signals from the O/E converting sections 241A, 242A into optical signals having the same wavelength with each other.
Namely, on the basis of the supervision control information that is input from the O/E converting sections 241A, 242A of the signal processing sections 241, 242, the optical switch controlling section 243 is adapted to the control optical switch 244 so as to select either one of the optical signal that has been transmitted through the path 301 (See A-path 310 in the Figure) and the optical signal that has been transmitted through the path 302 (See B-path 320 in the Figure), as an active optical signal.
Further, as illustrated in FIG. 5(a) and FIG. 5(b) in detail, the optical switch 244 includes a coil 244A and a prism 244B that can move so as to assume a position such as shown in FIG. 5(a) or FIG. 5(b) in accordance with the direction of a magnetic field by the coil 244A.
Namely, by a pulse signal from the optical switch controlling section 243, when the magnetic field inside the coil 244A is in a state of U direction shown in FIG. 5(a), a signal from the path 301 is outputted, while when the magnetic field inside the coil 244A is in a state of D direction shown in FIG. 5(b), a signal from the path 302 is outputted. Here, in the optical switch controlling section 243, the switching state of the optical switch 244 is retained by outputting only one pulse signal. Therefore, electric current is not let to flow through the coil 244A after the switching operation of the optical switch 244.
According to such a configuration, either one of the optical signals transmitted redundantly through the A-path 310 and the B-path 320 in the WDM transmitting apparatus 100 shown in FIG. 4 is selectively outputted by the switching control of the optical switch 244 by the optical switch controlling section 243.
Further, the optical switch controlling section 243 receives alarming information (for example, optical input cut-off, line errors, and the like) of the A-path and the B-path 320 as supervision control information that is detected respectively in the O/E converting sections 241A, 242A of the signal processing sections 241, 242 and, when it is determined that abnormality has occurred in a receiving path, switches the path to be selected by outputting a pulse signal to the optical switch 244.
Further, FIG. 6 is a view for describing the second mode of protection control in a conventional WDM transmission. In this FIG. 6, numeral 100 represents a WDM transmitting apparatus similar to the above-described one of FIG. 4, and numeral 200′ represents a WDM receiving apparatus having a different method of switching control of the paths 301, 302 compared with the above-described WDM receiving apparatus 200. Also, in a manner similar to the above-described case of FIG. 4, two paths 301, 302 for protection control are provided in the optical transmission direction from the WDM transmitting apparatus 100 towards the WDM receiving apparatus 200′.
Here, the WDM receiving apparatus 200′ includes the wavelength separating sections 231, 232 similar to those shown in FIG. 4 and n receiving-side protection processing sections 240′-1 to 240′-n that perform protection control that is different from the one shown in FIG. 4 (See reference numbers 240-1 to 240-n). Here, in the following, with respect to the configuration of the receiving-side protection processing sections 240′-1 to 240′-n, description will be given by keeping an eye on the receiving-side protection processing section 240′-1.
Here, the receiving-side protection processing section 240′-1 is configured to include signal processing sections 241′, 242, an optical switch controlling section 243′, and an optical coupler 244′.
Further, the signal processing sections 241′, 242′ respectively include the O/E converting sections 241A, 242A that convert the optical signals from the wavelength separating sections 231, 232 into electric signals and extract supervision control information needed for protection control to supply to the optical switch controlling section 243, and the E/O converting sections 241B, 242B that convert the electric signals from the O/E converting sections 241A, 242A into optical signals by receiving ON/OFF control of light from the optical switch controlling section 243.
FIG. 7 is a view illustrating a construction of an essential part of the above-described E/O converting sections 241B, 242B. As illustrated in this FIG. 7, the E/O converting sections 241B, 242B respectively include LD (Laser Diode) 245A, 245B, driving sections 247A, 247B that drive the LD 245 by electric signals from the O/E converting sections 241A, 241B using power source 246 as a voltage supplying source, and switches 248A, 248B that control supply/non-supply of a voltage signal supplied from the power source by a controlling signal from the optical switch controlling section 243.
Namely, the switches 248A, 248B are controlled by the controlling signal from the optical switch controlling section 243 to supply the electric signal from the power source 246 to the LD 245A, 245B for the E/O converting section 241B, 242B on the selected path side (active state), and not to supply the electric signal from the power source 246 to the LD 245A, 245B for the E/O converting section 241B, 242B on the non-selected path side (non-active state).
This allows that the optical switch controlling section 243 can control the E/O converting sections 241B, 242B so as to select either one of the optical signal transmitted through the path 301 (A-path 310 in the Figure) and the optical signal transmitted through the path 302 (B-path 320 in the Figure) as an active optical signal on the basis of the supervision control information inputted from the O/E converting sections 241A, 242A of the signal processing sections 241, 242.
With such a configuration, either one of the optical signals that have been transmitted redundantly through the A-path or the B-path in the WDM transmitting apparatus 100 shown in FIG. 6 is selectively outputted by switching control of active state/non-active state of the E/O converting sections 241B, 242B by the optical switch controlling section 243.
However, in the above-described apparatus 200 for protection control shown in FIG. 4, the active path is selected by the pulse signal supplied to the optical switch 244, so that the electric current does not flow through the coil after the switching operation of the optical switch 244, making it impossible to confirm in which direction the optical switch is operating correctly after the switching operation. Namely, there is a problem in that one cannot confirm which of the A-path and the B-path is selected.
Further, in the apparatus 200′ for protection control shown in FIG. 6, the active path is selected by active/non-active of the LD 245A, 245B in the E/O converting sections 241B′, 242B′. For example, when the LD 245A, 245B of the E/O converting section 241B′, 242B′ in the standby path is out of order, these LD 245A, 245B cannot be activated even if a controlling signal for activating the LD 245A, 245B of the E/O converting section 241B′, 242B′ in the standby path is outputted in the optical switch controlling section 243′, thereby raising a problem. In other words, in the protection mode of FIG. 6, since the standby system is in a non-active state, the normality of the standby system cannot be supervised.
Meanwhile, as a known art related to the invention of the present application, there is one disclosed in Japanese Patent Application Laid-Open HEI8-125636. In order to realize a protection method which is rapid and certain in wavelength multiplexing transmission, a transmission apparatus disclosed in this Japanese Patent Application Laid-Open HEI8-125636 is provided with means for detecting an obstacle for the signal of each wavelength and means for switching the signals transmitted by being subjected to wavelength multiplexing through one active transmission path simultaneously to a standby transmission path.
However, in the transmission apparatus disclosed in this Japanese Patent Application Laid-Open HEI8-125636, the above-described means for switching to the standby transmission path is constituted of a selector or a spatial switch controlled by a controlling circuit. However, no specific disclosure is given on the construction of the selector, so that when it is constructed as shown in the above-described FIG. 5(a) or FIG. 5(b), it seems to be difficult to monitor the path selection direction at all times.
The present invention has been devised in view of such a problem, and an object thereof is to provide a transmission apparatus and a path selection method of a transmission apparatus that can always monitor the path selection direction by an optical switch and also can always supervise the normality of a standby system which is a non-selected optical path.